What can play the role of gluten in gluten free pasta? 1
Alessandra Martiand Maria Ambrogina Pagani*
2
Department of Food, Enviromental, and Nutritonal Sciences - DeFENS, Università degli Studi di 3
Milano, via G. Celoria 2, 20133 Milan, Italy 4
* corresponding author: Maria Ambrogina Pagani
5
ambrogina.pagani@unimi.it 6
Tel.: +39 02 50316658. 7
via G. Celoria 2, 20133 Milan, Italy
Highlights 9
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The strategies used for the replacement of gluten functionality in pasta were reviewed10
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The effects of treatments on raw-materials were examined11
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The effects of processing conditions on starch properties and pasta quality were considered12 13
14
ABSTRACT: 15
Defining and optimizing the technological process to improve the sensory and nutritional 16
characteristics of gluten-free (GF) products still represent a challenge for researchers and industry. 17
As regards pasta, several ingredients (modified starch, GF flours, additives) have been used as 18
alternatives to gluten in order to create a starchy network that can withstand the physical stresses of 19
cooking and impart firmness to the cooked product. Moreover, different variations of noodle-20
making technology have been proposed to simplify the artisan process based on repeated heating 21
and cooling steps, which are difficult to control and monitor. This paper will overview how to 22
replace gluten functionality in GF pasta. 23
INTRODUCTION 25
The popularity of pasta is increasing worldwide, thanks to its convenience, palatability, long and 26
easy shelf-life, and, last but not least, its nutritional properties. In addition to the conventional pasta-27
product made from durum wheat semolina, it is common to enrich pasta with some cereals (barley, 28
rye, etc.), pseudocereals (buckwheat, amaranth, quinoa), and legume flours (pea, chickpea, etc.), to 29
provide sources of fiber, minerals, antioxidants, and polyphenols. In the last few decades, a third 30
group of pasta-products, the gluten-free (GF), is being consumed not only by the growing number 31
of celiacs but also by others who wish to exclude gluten-based products from their diet for health 32
reasons. Moreover, as celiac disease can occur at any age, the production of good quality GF 33
products for people with a tradition consuming of wheat-based products is necessary as an 34
alternative. Currently, there is a broad variety of GF products available for celiacs made from rice, 35
corn, and other GF flours. Unfortunately, most of them exhibit poor cooking quality, particularly 36
when compared with their wheat counterparts (Hager, Zannini & Arendt, 2012; Lucisano, Cappa, 37
Fongaro & Mariotti, 2012). Moreover, many GF products are nutritionally inferior, i.e. poorer in 38
minerals and bio-components, to the wheat-based foods they are intended to replace. These findings 39
suggest that more attention should be paid to the nutritional and sensory quality of GF products. At 40
this regard, recently, the possibility of using green banana flour to produce pasta products with 41
bioactive compounds, such as resistant starch and phenolic acids, was also investigated by 42
Zandonadi et al. (2012). Although the demand for better-tasting, better-textured, and healthier GF 43
products offers great market opportunities for food manufacturers, the replacement of gluten 44
functionality still presents a major technological challenge. The degree of difficulty in producing 45
GF products is closely associated with the technological role of gluten in the food-system. Cookies, 46
whose texture mainly depends on sugar and fat to assure crispness and friability, are the easiest to 47
formulate without gluten because it plays a secondary role in their making and end-product quality 48
(Engleson & Atwell, 2008). The most challenging products to formulate and produce are GF bread 49
and pasta, as gluten is their architectural key. The few papers published in the last decade (FSTA 50
database) on GF pasta (about 20, excluding patents) indicates the difficulty of this task. 51
GLUTEN FUNCTIONALITY IN PASTA FROM DURUM-WHEAT SEMOLINA 52
Pasta is considered one of the simplest cereal-based products in terms of ingredients (only two: 53
semolina and water) and processing (a sequence of hydration, mixing, forming, and drying steps). 54
Both raw-material characteristics and processing conditions play a key role in determining the 55
quality of final pasta products (De Noni & Pagani, 2010). Protein quantity and quality have 56
received considerable attention as the most important factors affecting pasta properties (D’Egidio, 57
Mariani, Nardi, Novaro & Cubadda, 1990). A high protein content and a “strong” gluten (in terms 58
of its visco-elasticity) are required to process semolina into a suitable final pasta product with an 59
optimal cooking performance (D’Egidio, Mariani, Nardi, Novaro & Cubadda, 1990; Feillet & 60
Dexter, 1996). Microscopic observations have revealed that the gluten network in dried pasta is 61
more or less uniformly and regularly arranged around starch granules according to the quality of the 62
semolina used (Resmini & Pagani, 1983). On the contrary, starch in dried pasta is still in the form 63
of whole native granules, as in semolina. During cooking, starch and protein exhibit completely 64
different behaviors. The starch granules rapidly swell, tend to disperse, and become partly soluble. 65
While, proteins become completely insoluble and coagulate, creating a strengthened network, which 66
traps starch material (Resmini & Pagani, 1983). Starch gelatinisation and protein coagulation are 67
both competitive phenomena, occur at the same temperature and are influenced by water 68
availability (Pagani, 1986). The faster the formation of a continuous protein network, the more 69
limited the starch swelling, thus ensuring firm consistency and the absence of stickiness in pasta 70
(Resmini & Pagani, 1983). On the contrary, if the protein network lacks elasticity or its formation is 71
delayed, starch granules will easily swell, and part of the starchy material will pass into the cooking 72
water, resulting in a product characterized by stickiness and poor consistency (Resmini & Pagani, 73
1983). 74
HOW TO REPLACE GLUTEN FUNCTIONALITY IN GLUTEN FREE PASTA 75
While gluten proteins play a key role in conventional semolina pasta properties, starch is the 76
determining component in GF pasta only if it can re-organize the macromolecular structure in an 77
efficacious way giving a texture similar to that found in semolina products. Pasta companies can 78
adopt different approaches to reach this goal. In any case, starch has to assume a structuring role, 79
which is related to the tendency of its macromolecules to re-associate and interact after 80
gelatinization, resulting in newly organized structures that retard further starch swelling and 81
solubilisation during cooking. Despite this well known fact, few studies have dealt with starch 82
organization in GF pasta. In the late ‘80s, Mestres, Colonna & Buleon (1988) investigated the starch 83
network of GF noodles using DSC and X-rays, and found that new crystalline organizations were 84
formed as a consequence of starch retrogradation. Amylose-based structures were present in 85
retrograded form (B-type) and the good cooking behaviour of rice noodles was mainly attributed to 86
amylose networks. More recently, Marti, Seetharaman, & Pagani (2010) and Marti, Pagani & 87
Seetharaman (2011a,b) observed that the average molecular weight of amylose and amylopectin, as 88
well as their molecular organization within the granule, affected starch functionality and, 89
consequently, cooking performance. 90
Basically, in GF pasta, the role of gluten could be replaced by choosing suitable formulations and 91
recipes using heat-treated flours as the key-ingredients, or by adopting non-conventional pasta-92
making processes to induce new rearrangements of starch macromolecules. 93
GLUTEN-FREE PASTA FORMULATION 94
The common ingredients in GF pasta are flour and/or starch from corn, rice, potato (or other 95
tubers), with the addition of protein, gums, and emulsifiers which may partially act as substitutes 96
for gluten. The diversity of GF raw materials help to increase the quantity and the quality of 97
products for celiacs. 98
Formulating GF pasta requires, firstly, a thorough knowledge of the component properties of GF 99
flours and starches. Then, appropriate additives may be selected to promote a cohesive mass in the 100
product. 101
THE PROPERTIES OF GLUTEN FREE STARCHY FLOURS 102
The ideal starch for GF pasta products should have a marked tendency to retrograde: this property, 103
generally observed in high amylose cereals and pulses, assures good cooking behaviour in terms of 104
texture and low cooking loss, even after prolonged cooking (Lii & Chang, 1981; Bhattacharya, Zee 105
& Corke, 1999). Mung bean starch is considered one of the best raw material for producing high 106
quality starch spaghetti, due to its high amylose content and type C viscoamylogram pasting profile, 107
characterized by the absence of a peak and the presence of a constantly increasing viscosity during 108
heating and shearing, indicative of good hot-paste stability (Lii & Chang, 1991). 109
Today, GF flours are used more than starches, thus skipping the expensive stage of starch extraction 110
from the grains. Furthermore, from a technological point of view, the use of flours allows to exploit 111
the presence of interactions between starch and other components, such as proteins and lipids. 112
Despite scientific efforts to determine the physico-chemical properties of GF raw materials as they 113
relate to the final quality of noodles (Bhattacharya; Zee & Corke, 1999; Tam, Corke, Tan, Li & 114
Collado, 2004), the selection of raw-materials for GF pasta production is currently based solely on 115
checking for the absence of gluten, while neglecting the evaluation of starch characteristics of GF 116
flours. In fact, GF industries prefer using peculiar heat-treatments or additives for improving the 117
cooking behaviour of GF pasta products. 118
Rice
119
Rice (as flour or starch) is present in practically all GF products in the market. Frequently rice flour 120
is produced starting from broken grains which are removed during milling since they decrease the 121
commercial quality of whole grain rice. 122
Traditional rice noodles are made from long-grain rice flour with intermediate-to-high amylose 123
content (> 22 g/100 g), which plays a pivotal role in creating a starch network in rice noodles 124
(Kohlwey, Kendall & Mohindra, 1995). Several studies have assessed the quality of noodles made 125
from different rice varieties. On the basis of sensory evaluation, Sanchez (1975) found a highly 126
significant correlation between high amylose content and panel acceptability. Chen & Luh (1980) 127
reported that the swelling capacity of starch and amylose-amylopectin ratio are the two major 128
factors affecting rice noodle quality. Li & Luh (1980) noted that rice varieties with high amylose 129
content, low gelatinisation temperature, and hard gel consistency were best suited for making 130
noodles. These findings were confirmed some years later, when a good correlation between 131
physico-chemical properties and the texture of vermicelli was found (Bhattacharya; Zee & Corke, 132
1999). 133
Little attention has actually been paid to flour from brown rice, despite its high nutritional value 134
related to dietary fibre, phytic acid, vitamins E and B, and aminobutyric acid (GABA): these 135
components are present in relevant quantities in the bran layers and germ which are removed during 136
the polishing (or milling step) to obtain milled rice. Recently, Marti, Seetharaman & Pagani (2010) 137
prepared GF pasta from brown rice flour. The higher fibre content in brown rice was responsible for 138
a weakening of the starch network and consequently for the increase in cooking loss. At the same 139
time, the inclusion of fibre in the starch matrix partially reduced the extreme firmness and 140
springiness found in pasta from milled rice flour. 141
Corn
142
Amylose in corn noodles has also been indicated as the component accounting for their textural 143
integrity after cooking. Dexter & Matsuo (1979) showed that in corn blends, the lower the amylose 144
content, the lower the noodle cooking quality. However, corn starches with high amylose contents 145
(>40%) don’t provide a sufficient degree of gelatinisation during the heating process, limiting the 146
extent of the following starch retrogradation (Tam, Corke, Tan, Li & Collado, 2004). Corn starches 147
with amylose contents of around 26-28% were successfully used for bihon-type noodle production 148
(Tam, Corke, Tan, Li & Collado, 2004). 149
Mestres, Colonna, Alexandre & Matencio (1993) studied the effects of various heat-treatments 150
(drum-drying, extrusion-cooking, pasting with hot water, or steaming) on corn pasta properties. The 151
best cooking quality was observed using the drum-drying process, even if no reason was given. 152
Waniska et al. (1999) investigated the effects of several parameters on corn noodle quality. 153
Preheating the mixture of corn flour and water (43-45% moisture) at 90-95 °C was required to 154
successfully extrude noodles using a pasta-maker. Adding more water to noodle production resulted 155
in higher gelatinisation, which is associated with longer cooking times and lower cooking losses 156
(Waniska et al., 1999). 157
Sorghum
158
The grain presents interesting characteristics from a nutritional standpoint, as it is a source of 159
protein, starch, and antioxidant compounds. For this reason, a potential novel use of sorghum could 160
be the manufacture of pasta products, in addition to or as a substitute for corn or rice flours in the 161
preparation of GF food. 162
Suhendro, Kunetz, McDonough, Rooney & Waniska (2000) investigated the effect of the cultivar, 163
flour particle size, and processing conditions on the cooking quality of noodles prepared from flour 164
of decorticated sorghum on laboratory scale. The fine flour preheated in a microwave oven and 165
dried using the two-stage method produced the best noodles with moderate dry matter loss. Noodles 166
from waxy sorghum proved to be of inferior quality compared to normal sorghum. Such noodles 167
were soft and sticky, with high losses during cooking, probably as a consequence of limited 168
retrogradation extent (Suhendro, Kunetz, McDonough, Rooney & Waniska, 2000). 169
Recently, flour from fermented sorghum was mixed to brown rice flour to prepare GF pasta (Pagani 170
et al., 2010). The modification of the structural and physical properties promoted by fermentation
171
improved pasta quality with respect to the sample from unfermented sorghum. 172
Pseudo-cereals
173
Amaranth, quinoa, and buckwheat are becoming increasingly popular because they improve the 174
nutritional quality of GF products, in terms of high fibre, vitamins, minerals, and other bioactive 175
components (polyphenols, phytosterols, etc.) (Alvarez-Jubete, Arendt & Gallagher, 2010). Despite 176
the few published data on oat-enriched GF pasta, oat flour is not commonly used as ingredients for 177
GF formulations. In fact, a number of early studies produced conflicting results and most 178
gastroenterologists have been cautious and recommended avoidance of oats.
179
Good quality spaghetti were produced from blends of corn, soy, oat, and quinoa (5-15%) flours 180
(Caperuto, Amaya-Farfan & Camargo, 2001; Chillo et al., 2009; Mastromatteo, Chillo, Iannetti, 181
Civica & Del Nobile, 2011). GF macaroni from blends of quinoa and rice flour obtained by 182
extrusion at 60 and 77 °C have also been successfully produced (Borges, Ramirez Acheri, Ramirez 183
Ascheri, Do Nascimento & Freitas, 2003). By blending buckwheat, amaranth, and quinoa in 184
different ratios by means of an experimental design (along with the addition of albumen, emulsifier, 185
and enzymes), Schoenlechner, Drausinger, Ottenschlaeger, Jurackova & Berghofer (2011) 186
improved the cooking quality of GF pasta. The best product was prepared from a combination of 187
amaranth, quinoa, and buckwheat (40:40:60), with 6% of egg white powder and 1.2% of emulsifier. 188
More recently, Cabrera-Chávez et al. (2012) prepared amaranth-supplemented GF pasta, observing 189
that the incorporation of amaranth to rice flour (25:75 ratio), combined with the cooking-extrusion 190
process, improved the nutritional quality of pasta, while maintaining good cooking behaviour. 191
THE USE OF ADDITIVES AND TEXTURING INGREDIENTS 192
Pasta prepared only from non-gluten flour is generally considered to be inferior in textural quality 193
compared to semolina pasta: it does not tolerate overcooking, it is sticky, and, above all, it is 194
characterized by relevant cooking losses. Adding texturing ingredients can be a simple solution for 195
improving pasta cooking behaviour by decreasing these defects. 196
Hydrocolloids or gums are commonly used for their ability to make a gel in little quantities, provide 197
high consistency at room temperature, improve firmness, give body and mouthfeel to pasta. In 198
addition, because of their ability to bind water, gums can increase the rehydration rate of pasta 199
(Sozer, 2009). A wide range of hydrocolloids have been proposed: arabic gum, xanthan-gum, locust 200
bean gum, carboxymethylcellulose (CMC), etc. 201
Emulsifiers act as lubricants in the extrusion process and provide firmer consistency and a less 202
sticky surface, as they control starch swelling and leaching phenomena during cooking (Lai, 2002), 203
thereby improving the texture of the final product (Kaur, Singh & Singh., 2005; Charutigon, 204
Jitpupakdree, Namsreem & Rungsardthong, 2008). 205
Despite the several well-known positive effects of the addition of emulsifiers and hydrocolloids 206
(Huang, Knight, & Goad 2001; Lai, 2002; Singh, Raina, Bawa & Saxena, 2004; Kaur, Singh & 207
Singh., 2005; Chillo, Laverse, Falcone & Del Nobile, 2007; Charutigon, Jitpupakdree, Namsreem & 208
Rungsardthong, 2008; Sozer, 2009) consumers often associate their presence in GF pasta to an 209
“artificial” food. Consequently, the use of proteins as structuring building ingredients represents an 210
interesting alternative for producing GF pasta, not to mention its positive nutritional effects 211
(Thompson, 2009). In this regard, recent studies found an improvement in pasta texture when egg 212
and milk proteins were used in GF formulations (Chillo et al., 2009; Sozer, 2009; Schoenlechner, 213
Drausinger, Ottenschlaeger, Jurackova & Berghofer, 2011). 214
THE OPTIMIZATION OF GF PASTA-MAKING PROCESS 215
Up to now, GF pasta made from solely GF flour has usually been prepared in one of two ways. The 216
first approach focuses on the use of heat-treated flours, in which starch is already mostly 217
gelatinized. Here, the pre-treated flour can be formed into pasta by the continuous extrusion press 218
commonly used in durum wheat semolina pasta-making. In the second technological approach 219
(extrusion-cooking process), native flour is treated with steam and extruded at high temperatures 220
(more than 100°C) for promoting starch gelatinization directly inside the extruder-cooker. Marti, 221
Caramanico, Bottega & Pagani (2012) applied both these processes to native rice flour, without 222
additives or structuring ingredients. Because a regular and continuous protein network was lacking, 223
starch polymers were less efficaciously entrapped in the rice matrix, resulting in a product with high 224
cooking losses (10g/100g), two-three times higher than those of pasta from durum wheat semolina. 225
As regards the texture, pasta prepared from pre-gelatinized flour (Pasta A) exhibited higher 226
firmness compared to that of pasta from extrusion-cooking of native flour, using a single-screw 227
extruder (Pasta B). The ultrastructure images reported in Figure 1 highlighted differences in starch 228
arrangement inside the two products. At the beginning of cooking, Pasta A showed a compact and 229
homogeneous matrix (Figure 1a). On the contrary, the mere immersion of Pasta B in hot water 230
induced a great disruption of surface structure (Figure 1b), accounting for the high water absorption 231
(91 g/100g and 78g/100g, by Pasta B and Pasta A, respectively) and the low firmness (190 N and 232
310 N for Pasta B and Pasta A, respectively). In addition, the extrusion-cooking of native rice was 233
not efficacious in creating a continuous and smoothed starchy matrix, since some aggregates are 234
still recognizable (Figure 1c). 235
Recently, Chillo et al. (2010) investigated the effect of the repeated extrusion steps (at temperatures 236
below 46°C) on the sensory characteristics of GF spaghetti. This processing promoted the formation 237
of a compact structure in the dried product. But, the application of shear stress without the 238
combination of high temperature was not efficacious in promoting starch gelatinisation, and thus 239
there was no improvement in the sensory quality of the cooked pasta. 240
Careful selection of processing conditions is the starting point for promoting new starch 241
arrangements in GF raw materials to assure good cooking behaviour and effective structure, not 242
only for the texture but also for nutritional properties in terms of enzyme accessibility and starch 243
digestibility. 244
FROM TRADITIONAL NOODLE-MAKING PROCESS TO THE CURRENT
GF pasta-making is still based on ancient but still-in-use processes for making Oriental starch 247
noodles. As the main ingredient of GF raw-materials, starch plays a key role in noodle production. 248
Non-gluten noodle-technology is mainly based on dough heating and cooling operations, that 249
exploit two phenomena: firstly starch gelatinisation and, then, its retrogradation. The greater the 250
degree of starch gelatinisation, the better the cooking quality. On the contrary, a slight starch 251
swelling is related to pasta disruption during cooking due to the lack of a continuous network of 252
retrograded starch (Pagani, 1986). For this reason the traditional noodle-making process suggests 253
heat-treatments at high temperatures (90-95 °C) during extrusion, which may be repeated several 254
times (Tan, Li & Tan, 2009). During the cooling steps, new and spontaneous starch crystallization 255
occurs, resulting in a translucent, vitreous, and consistent product. These modifications promote a 256
loss of starch granular structure during gelatinisation, and an extensive reticular and fibrillar 257
network after cooling (Resmini & Pagani, 1983). 258
Even if the highly reticulated starch network can account for the good cooking quality of the 259
artisanal pasta, traditional Oriental noodle-technology is difficult to transfer to an industrial scale. 260
Controlling gelatinisation and retrogradation phenomena is hard and requires many hours of work 261
and high amounts of energy and water to heat and cool the dough. Moreover, the size or the 262
diameter of the product is a critical factor: the thin layer of noodles (diameter of 0.68-0.78 mm) is 263
essential in decreasing the sensory perception of extreme hardness and springiness in a product 264
characterized by a strong degree of retrogradation. 265
Considering all these disadvantages, the use of pre-heated flour or extrusion-cooking processed 266
flour bypasses the steps of the discontinuous process (steaming, cooking in boiling water, and 267
cooling), thus simplifying traditional noodle making technology. 268
EXTRUSION-COOKING PROCESS 269
Extrusion-cooking is one of the most suitable technologies for GF pasta-making. Extrusion-cooking 270
consists of using high temperature for a relatively short time, and is commonly used for producing 271
several food items (pre-gelatinized starch, snacks, ready-to-eat breakfast cereals, etc.). The main 272
phenomenon associated with the extrusion-cooking used and exploited in GF pasta-making is again 273
starch gelatinisation. In fact, starch granule organisation is disrupted to render it digestible and to 274
produce a malleable product. In other words, the crystalline starch macromolecules are converted 275
into a more amorphous material, as recently reported by Wolf (2010). 276
Tsao (1976) was one of the first authors to apply extrusion-cooking to make rice spaghetti. More 277
recently, the suitability of pea starch and pea flour for pasta-making using a twin-screw cooking-278
extruder was investigated (Wang et al., 1999; Vasanthan & Li, 2003). Pasta obtained by extrusion-279
cooking exhibited superior firmness, flavour, and texture after cooking, compared to pasta-products 280
prepared from the same flour using a conventional extruder (Wang et al., 1999). Extrusion-cooking 281
has been successfully used for pasta production from corn (Budelli & Fontanesi, 2007; Merayo, 282
Gonzalez, Drago, Torres & De Greef, 2011; Giménez et al., 2013). The GF flour was first heat-283
treated in an extruder by contact with a heated wall and/or steam injection, and then, extruded, 284
formed and shaped, and finally dried. A certain degree of cooking has to be reached so as to obtain 285
pasta with good cooking characteristics and resistance to overcooking (Merayo, Gonzalez, Drago, 286
Torres & De Greef, 2011; Giménez et al., 2013).
287
THE USE OF PRE-TREATED FLOURS 288
The use of pre-treated flours, whereby starch is disorganized by pre-cooking it in a separate plant 289
before pasta-making, is one of the processes currently used to prepare GF pasta. In this regard, 290
several heat-treatments have been proposed and each of them specifically affects starch properties 291
(Table 1). Physical treatments have also been applied to starches to alter their native 292
physiochemical properties in order to meet various industrial needs (Zavareze, Storck, de Castro, 293
Schirmer & Dias, 2010). Understanding the nature of the changes could help determine the choice 294
of efficacious treatments on starch for the GF pasta sector. 295
Annealing (ANN), consisting in the treatment of starch in excess of water (more than 40%) at a 296
temperature below gelatinisation (for rice 50-60°C), and heat-moisture treatment (HMT; treatment 297
at low moisture and high temperatures, 100-120°C for rice) are hydrothermal processes often used 298
in modifying the native physiochemical properties of starch (Jacobs & Delcour, 1998). Both ANN 299
and HMT increase starch crystallinity, granule rigidity, and polymer chain associations (Jacobs & 300
Delcour, 1998; Tester & Debon, 2000). These particular hydrothermal treatments suppress granule 301
swelling, retard gelatinization, and increase starch paste stability (Hoover & Vasanthan, 1994; 302
Hormdok & Noomhorm, 2007), thus improving cooking behaviour and texture properties of rice 303
noodles (Yoenyongbuddhagal & Noomhorm, 2002; Hormdok & Noomhorm, 2007). In addition, 304
Cham & Suwannaporn (2010) optimized hydrothermal treatment conditions to obtain rice noodles 305
exhibiting different cooking qualities. ANN is suitable for preparing fresh rice noodles that require 306
a soft texture, whereas HMT is more appropriate for semi-dried and dried noodles characterized by 307
high tensile strength and gel hardness. 308
Despite the improvements associated with the use of ANN and HMT flours, the use of pre-309
gelatinized flour is generally considered a cheaper approach for improving rice noodle quality. 310
Raina, Singh, Bawa & Saxena, (2005) reported that the textural quality of both uncooked and 311
cooked pasta improved significantly when pre-gelatinized rice flour was used. Moreover, the 312
intensity of flour pre-gelatinisation plays a very important role in imparting a desirable noodle 313
texture. Although gelatinisation is required to produce the binding effect during extrusion, excessive 314
gelatinisation may cause extremely high extrusion pressures (Juliano & Sakurai 1985). More 315
recently, Yalcin & Basman (2008a) investigated the effect of the gelatinisation level of rice flour on 316
noodle cooking behaviour. Samples obtained with 25% gelatinisation level exhibited lower cooking 317
loss and better tolerance during cooking compared to samples prepared with 15, 20, or 30% 318
gelatinisation level. Other works noted that the effects of gelatinisation extent on the final product 319
depended on the cereal variety and processing conditions used. In the case of corn, noodles 320
Basman, 2008b). The hydration level and the time-temperature conditions of the pre-gelatinisation 322
process significantly affected the pasta-making process and the cooking quality of rice pasta (Lai, 323
2002). Low hydration level (400g water/kg flour) and steaming for short times and low 324
temperatures (85°C for 10 min) resulted in the formation of rice dough that easily extruded into 325
pasta. On the contrary, rice dough prepared using a high hydration level and high gelatinisation was 326
too viscous to be extruded (Lai, 2002). More recently, Marti (2010) reported that the substitution of 327
50% rice flour with pre-gelatinized flour improved the quality of the pasta. These authors supposed 328
that the pre-gelatinized flour may have acted as a binder, re-polymerizing into a network around the 329
starch granules of rice flour during the extrusion step, because of the different gelatinization 330
temperatures of the two flours, thereby increasing their tolerance to cooking stress, as Pagani (1986) 331
suggested too. 332
Pre-gelatinized flours is currently preferred by GF pasta companies also because it can be used in 333
the same conventional press for semolina pasta. However, some technological know-how has to be 334
used. In GF pasta production, the amount of water added to the pre-gelatinized flour has to 335
calculated by taking into account the higher water affinity of this raw-material. Generally, the final 336
moisture of dough could amount to 40% of the mixture (Marti, Seetharaman & Pagani, 2010), 337
higher than in semolina dough (approximately 30% moisture; Dalbon, Grivon & Pagani, 1996). 338
Recently, Grugni, Mazzini, Viazzo & Viazzo (2009) patented the use of parboiled rice in GF pasta 339
production. Parboiling, carried out on paddy rice, promotes changes in the physicochemical, 340
nutritional, and sensory properties of the kernel: starch gelatinizes, part of the vitamins and minerals 341
migrate towards the endosperm, and a lipid-amylose complex is formed, restricting starch swelling 342
and amylose leaching during cooking (Bhattacharya, 2004). These modifications on starch 343
organization are responsible for decreasing stickiness and increasing hardness of the cooked kernels 344
(Bhattacharya, 2004). Marti, Seetharaman & Pagani (2010) demonstrated that the use of flour from 345
parboiled rice promoted the formation of a new macromolecular structure, resulting in good texture 346
after cooking, also according to the parboiling conditions (steeping temperature) (Marti, 347
Seetharaman & Pagani, 2010; Marti, 2010). Further, the strong interactions of amylopectin and/or 348
amylose promoted by the extrusion-cooking process suggested that the amylopectin matrix is likely 349
a combination of amylose and amylopectin chains. By using parboiled rice flour, the traditional 350
recipe for producing pasta (flour and water) are maintained, while additives (such as modified 351
starches, gums, mono and diglycerides of fatty acids, etc.) are avoided. 352
CONCLUSIONS 353
Despite the great efforts made in the last few decades to produce GF pasta with sensory 354
characteristics similar to durum wheat products, the GF pasta currently on the market is still far 355
from what the consumer is looking for. Moreover, little information is available regarding starch 356
arrangements that can guarantee good quality cooking. In fact, up-to-now only a few works have 357
investigated the molecular starch organizations induced by different treatments and how these 358
impact on pasta cooking behaviour. Most studies adopt an empiric approach: varying ingredients 359
and processing conditions rather than understanding the macromolecule organization associated 360
with good or poor cooking quality. Moreover, most of the few studies published refer to laboratory 361
scale pasta-making, neglecting its transfer to an industrial scale. Understanding the relationship 362
between starch structure and processing conditions will help the industry re-formulate and develop 363
products with the desired texture as well as improved nutritional and digestive properties. 364
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